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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.4.
package org.bouncycastle.crypto.encodings;
import java.security.SecureRandom;
import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.CryptoServicesRegistrar;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.ExtendedDigest;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.util.DigestFactory;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.Bytes;
import org.bouncycastle.util.Memoable;
import org.bouncycastle.util.Pack;
/**
* Optimal Asymmetric Encryption Padding (OAEP) - see PKCS 1 V 2.
*/
public class OAEPEncoding
implements AsymmetricBlockCipher
{
private static int getMGF1NoMemoLimit(Digest d)
{
if (d instanceof Memoable && d instanceof ExtendedDigest)
{
return ((ExtendedDigest)d).getByteLength() - 1;
}
return Integer.MAX_VALUE;
}
private final AsymmetricBlockCipher engine;
private final Digest mgf1Hash;
private final int mgf1NoMemoLimit;
private final byte[] defHash;
private SecureRandom random;
private boolean forEncryption;
public OAEPEncoding(
AsymmetricBlockCipher cipher)
{
this(cipher, DigestFactory.createSHA1(), null);
}
public OAEPEncoding(
AsymmetricBlockCipher cipher,
Digest hash)
{
this(cipher, hash, null);
}
public OAEPEncoding(
AsymmetricBlockCipher cipher,
Digest hash,
byte[] encodingParams)
{
this(cipher, hash, hash, encodingParams);
}
public OAEPEncoding(
AsymmetricBlockCipher cipher,
Digest hash,
Digest mgf1Hash,
byte[] encodingParams)
{
this.engine = cipher;
this.mgf1Hash = mgf1Hash;
this.mgf1NoMemoLimit = getMGF1NoMemoLimit(mgf1Hash);
this.defHash = new byte[hash.getDigestSize()];
hash.reset();
if (encodingParams != null)
{
hash.update(encodingParams, 0, encodingParams.length);
}
hash.doFinal(defHash, 0);
}
public AsymmetricBlockCipher getUnderlyingCipher()
{
return engine;
}
public void init(boolean forEncryption, CipherParameters param)
{
SecureRandom initRandom = null;
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
initRandom = rParam.getRandom();
}
this.random = forEncryption ? CryptoServicesRegistrar.getSecureRandom(initRandom) : null;
this.forEncryption = forEncryption;
engine.init(forEncryption, param);
}
public int getInputBlockSize()
{
int baseBlockSize = engine.getInputBlockSize();
if (forEncryption)
{
return baseBlockSize - 1 - 2 * defHash.length;
}
else
{
return baseBlockSize;
}
}
public int getOutputBlockSize()
{
int baseBlockSize = engine.getOutputBlockSize();
if (forEncryption)
{
return baseBlockSize;
}
else
{
return baseBlockSize - 1 - 2 * defHash.length;
}
}
public byte[] processBlock(
byte[] in,
int inOff,
int inLen)
throws InvalidCipherTextException
{
if (forEncryption)
{
return encodeBlock(in, inOff, inLen);
}
else
{
return decodeBlock(in, inOff, inLen);
}
}
public byte[] encodeBlock(byte[] in, int inOff, int inLen) throws InvalidCipherTextException
{
int inputBlockSize = getInputBlockSize();
if (inLen > inputBlockSize)
{
throw new DataLengthException("input data too long");
}
byte[] block = new byte[inputBlockSize + 1 + 2 * defHash.length];
//
// copy in the message
//
System.arraycopy(in, inOff, block, block.length - inLen, inLen);
//
// add sentinel
//
block[block.length - inLen - 1] = 0x01;
//
// as the block is already zeroed - there's no need to add PS (the >= 0 pad of 0)
//
//
// add the hash of the encoding params.
//
System.arraycopy(defHash, 0, block, defHash.length, defHash.length);
//
// generate the seed.
//
byte[] seed = new byte[defHash.length];
random.nextBytes(seed);
System.arraycopy(seed, 0, block, 0, defHash.length);
mgf1Hash.reset();
//
// mask the message block.
//
maskGeneratorFunction1(seed, 0, seed.length, block, defHash.length, block.length - defHash.length);
//
// mask the seed.
//
maskGeneratorFunction1(block, defHash.length, block.length - defHash.length, block, 0, defHash.length);
return engine.processBlock(block, 0, block.length);
}
/**
* @exception InvalidCipherTextException if the decrypted block turns out to
* be badly formatted.
*/
public byte[] decodeBlock(byte[] in, int inOff, int inLen) throws InvalidCipherTextException
{
// i.e. wrong when block.length < (2 * defHash.length) + 1
int wrongMask = getOutputBlockSize() >> 31;
//
// as we may have zeros in our leading bytes for the block we produced
// on encryption, we need to make sure our decrypted block comes back
// the same size.
//
byte[] block = new byte[engine.getOutputBlockSize()];
{
byte[] data = engine.processBlock(in, inOff, inLen);
wrongMask |= (block.length - data.length) >> 31;
int copyLen = Math.min(block.length, data.length);
System.arraycopy(data, 0, block, block.length - copyLen, copyLen);
Arrays.fill(data, (byte)0);
}
mgf1Hash.reset();
//
// unmask the seed.
//
maskGeneratorFunction1(block, defHash.length, block.length - defHash.length, block, 0, defHash.length);
//
// unmask the message block.
//
maskGeneratorFunction1(block, 0, defHash.length, block, defHash.length, block.length - defHash.length);
//
// check the hash of the encoding params.
// long check to try to avoid this been a source of a timing attack.
//
for (int i = 0; i != defHash.length; i++)
{
wrongMask |= defHash[i] ^ block[defHash.length + i];
}
//
// find the data block
//
int start = -1;
for (int index = 2 * defHash.length; index != block.length; index++)
{
int octet = block[index] & 0xFF;
// i.e. mask will be 0xFFFFFFFF if octet is non-zero and start is (still) negative, else 0.
int shouldSetMask = (-octet & start) >> 31;
start += index & shouldSetMask;
}
wrongMask |= start >> 31;
++start;
wrongMask |= block[start] ^ 1;
if (wrongMask != 0)
{
Arrays.fill(block, (byte)0);
throw new InvalidCipherTextException("data wrong");
}
++start;
//
// extract the data block
//
byte[] output = new byte[block.length - start];
System.arraycopy(block, start, output, 0, output.length);
Arrays.fill(block, (byte)0);
return output;
}
/**
* mask generator function, as described in PKCS1v2.
*/
private void maskGeneratorFunction1(byte[] z, int zOff, int zLen, byte[] mask, int maskOff, int maskLen)
{
int digestSize = mgf1Hash.getDigestSize();
byte[] hash = new byte[digestSize];
byte[] C = new byte[4];
int counter = 0;
int maskEnd = maskOff + maskLen;
int maskLimit = maskEnd - digestSize;
int maskPos = maskOff;
mgf1Hash.update(z, zOff, zLen);
if (zLen > mgf1NoMemoLimit)
{
Memoable memoable = (Memoable)mgf1Hash;
Memoable memo = memoable.copy();
while (maskPos < maskLimit)
{
Pack.intToBigEndian(counter++, C, 0);
mgf1Hash.update(C, 0, C.length);
mgf1Hash.doFinal(hash, 0);
memoable.reset(memo);
Bytes.xorTo(digestSize, hash, 0, mask, maskPos);
maskPos += digestSize;
}
}
else
{
while (maskPos < maskLimit)
{
Pack.intToBigEndian(counter++, C, 0);
mgf1Hash.update(C, 0, C.length);
mgf1Hash.doFinal(hash, 0);
mgf1Hash.update(z, zOff, zLen);
Bytes.xorTo(digestSize, hash, 0, mask, maskPos);
maskPos += digestSize;
}
}
Pack.intToBigEndian(counter, C, 0);
mgf1Hash.update(C, 0, C.length);
mgf1Hash.doFinal(hash, 0);
Bytes.xorTo(maskEnd - maskPos, hash, 0, mask, maskPos);
}
}
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